Near infrared electroluminescence from Nd(TTA)₃phen in solution-processed small molecule organic light-emitting diodes

We report on the near infrared electroluminescence properties of a Nd³⁺ complex with thenoyltrifluoroacetone and 1,10-phenantroline ligands in solution-processed organic light-emitting diodes. Spin-coated blends containing a 1,3-bis(9-carbazolyl)benzene host doped with the Nd³⁺ complex were found to exhibit a photoluminescence quantum yield of about 0.5%, regardless of the doping concentration level. Electroluminescent devices based on these small molecule blends showed the characteristic emission of Nd³⁺ at 890, 1060 and 1330 nm with an external quantum efficiency as high as 0.022%. These improved performances were mainly attributed to direct charge trapping and exciton formation on the near infrared emitter. Importantly, the efficiency roll-off at high current densities due to triplet-triplet exciton annihilation in the device containing 20 wt% of the complex was lower than what is typically observed in lanthanide complex-based electroluminescent devices. This is presumably due to the high triplet energy of the host material, which prevents guest-to-host energy-back transfer and thus host-guest triplet-triplet exciton annihilation.